1. Field of the Invention
The present invention relates to a production of thin films of a lead titanate system and, more particularly, a process of producing thin films of a lead titanate system useful as a material for electronic parts.
2. Description of the Prior Art
A ceramic material of a lead titanate system, expressed by the general formula: Pb(Zr.sub.x Ti.sub.1-x)O.sub.3, where 0.ltoreq.x&lt;1, possesses good properties required for a ferroelectric material, a piezoelectric material, or a pyroelectric material and has widely been used for various electronic parts such as, for example, ceramic capacitors, actuators and pyroelectric infrared sensors. With increasing demands for miniaturization and high performance of electronic equipments, it is common to use such a ceramic material of a lead titanate system in the form of thin film. To this end, there have been proposed various processes of producing thin films of ceramics, such as sputtering (JP-B-62-41311, JP-B- 63-238799), chemical vapor deposition (CVD, JP-A-63-178408), vacuum evaporation (JP-A-1-6306, JP-A-1-74778), cluster ion-beam process (JP-A-1-222046), plasma process (JP-A-2-57686), coating (JP-A-3-283583), fusion process (JP-A-60-84712), a sol-gel method (JP-A-26087), and hydrothermal synthesis (Proceeding papers, pp. 88-89, The eighth meetings of application of ferroelectrics). These processes may be divided into two groups, i.e., a vapor phase process in which the fabrication of thin films is carried out in a vapor phase, and a liquid phase process in which the fabrication of thin films is carried out in a liquid phase.
However, these processes have various problems awaiting a solution. For example, the vapor phase process (i.e., sputtering, chemical vapor deposition and vacuum evaporation, cluster ion-beam process, plasma process) requires use of complex and expensive equipment, resulting in considerable increase of production cost of the thin films. Further, the fabrication of the thin films is carried out in a gas stream of the raw materials, thus making is impossible to form thin films on the whole surface of the substrates, especially back of the substrate or on substrates with the complex configuration. In addition, there is a limit to the material of the substrates as the film fabrication is carried out at a high temperature.
On the other hand, in the liquid phase process, for example, the coating is too troublesome to operate as it requires coating and baking operations repeatedly. In addition, the coating process cannot be applied to substrates of a complex configuration. The sol-gel method has the disadvantage that it is inevitable to produce cracking in the thin film during firing. If the substrate has a many-tiered surface, it is difficult to produce uniform thin films. The hydrothermal method requires use of a substrate made of metallic titanium or coated with metallic titanium, thus making it difficult to increase applications thereof. In the fusion process in which a substrate with a fused solution is subjected to rapid cooling, there is a limit to the material of the substrates as the substrate is required to have a high heat resistance.